In recent years high-frequency signal generation circuits which generate signals (high-frequency signals), such as millimeter waves, having high frequencies have been used in radars and communication apparatus which perform radio communication.
With high-frequency signal generation circuits it is difficult to directly generate high-frequency signals, such as millimeter waves, by the use of a voltage controlled oscillator (hereinafter referred to as a VCO). Accordingly, after a signal whose frequency is comparatively low is generated by the use of a VCO, the frequency of the signal outputted from the VCO is multiplied by an integer by the use of a frequency multiplier. By doing so, a millimeter-wave carrier signal is obtained.
However, output power of the frequency multiplier is low, so a power amplifier is used for obtaining high output power. Furthermore, a gain amplifier is used for compensating for a change in the gain of the power amplifier or the like caused by a change in its temperature. In order to compensate for a change in the gain of the power amplifier or the like caused by a change in its temperature, a gain amplifier whose gain is high enough to make up for a drop in the gain of the power amplifier or the like is used. This increases power consumption.
Japanese Laid-open Patent Publication No. 62-47212
Japanese Laid-open Patent Publication No. 2009-165109
In order to check an increase in power consumption, an injection-locked oscillator (ILO) may be connected at a subsequent stage of the VCO. An injection-locked oscillator has the function of a frequency multiplier. In addition, output power of an injection-locked oscillator does not depend on the power of an input signal (referred to as an injected signal) and a change in output voltage of an injection-locked oscillator caused by a change in ambient temperature is slight. This avoids the necessity of using a gain amplifier which is used for compensating for a change in output voltage caused by a change in ambient temperature. As a result, power consumption is reduced.
If an injection-locked oscillator is used in a high-frequency signal generation circuit, a transistor whose gate width is narrow may be used in order to reduce parasitic capacitance. In that case, however, it is difficult to obtain high output power. In order to obtain high output power, a plurality of injection-locked oscillators may be connected in parallel and output of them may be combined. However, the power of an injected signal becomes lower and an operating band becomes narrower.